A thief is still a hunter and relies on many of the same skills, they just don't kill their prey (usually). Yes the forest is different from the slums, but many of the same skills still apply.

The twins are pickpockets, and we've only seen them fight, i think, once? The only reason they survived in the forest versus the molebadger was because of the Flupe, Klink thing and luck. They don't have any other weapons -- no super arms like Panthro (why he didn't use them is beyond me), a Staff like Cheetara (again, she only uses it when she thinks they're about to be attacked.) All the have is musical weapon and a grappling hook thing.